1. Field of the Invention
This invention relates to methods and devices for using light energy and photo-sensitive substances during the course of a drug therapy.
2. Description of the State of the Art
Photodynamic therapy (PDT) involves the delivery of chemical compound drugs called photosensitizers into tissue and then exciting the photosensitizer in order to enable an energy transfer from the photosensitizer to a nearby oxygen molecule. This produces an excited singlet state oxygen molecule that reacts with nearby bio-molecules. With respect to typical cardiovascular applications of PDT, this reaction causes localized damage in the target atherosclerotic tissue, thereby providing a beneficial effect to the patient.
Photochemical degradation occurs when a compound is exposed to high amounts of light which correspond to the absorbance band of the compound. The general mechanism for this degradation involves the absorption of light energy by electrons in chemical bonds. This energy causes the electrons to move to a higher energy state, which can produce a reactive region in the molecule. These reactive regions are more likely to interact with other compounds, notably oxygen, which can break or alter the chemical bond in the compound, resulting in an overall degradation of the chemical.